Many organic reactions involve the use of catalysts and particularly metal-containing catalysts. When utilizing these catalysts which may contain the metal in elemental form or as a metallic component, it becomes necessary to recover the catalyst or the metal contained therein in order to render the process economically viable. This is especially true when employing noble metals such as the noble metals of Group VIII of the Periodic Table including platinum, palladium, ruthenium, rhodium, osmium, iridium or other metals such as gold, silver, or rhenium. Due to the high cost of these metals, it is imperative that, as hereinbefore set forth, the loss of said metals be kept to a minimum in order to maintain the overall cost of the reaction at the lowest possible point. As an example of the type of organic reaction involving the use of a noble metal, a hydroformylation reaction may be cited. In this type of reaction, an olefinic hydrocarbon may be treated with carbon monoxide and hydrogen in the presence of a rhodium-containing compound which acts as the catalyst therefor in a one-step process to prepare an alcohol.
The commercialization of processes for the synthesis of alcohols utilizing a rhodium complex is affected by the difficulty which is attendant in the recovery of rhodium. A particular disadvantage which negates the commercial use of such complex catalysts comprises the frequent loss of the precious metal which may occur in process conditions. The loss of only a trace amount of this precious metal makes the process uneconomical to operate and overshadows the technological conversion rate and selectivity rate which is obtained when using this metal. The separation of the rhodium catalyst from alcohol products, especially high molecular weight alcohols, by conventional means such as distillation is not practical inasmuch as the unstable rhodium complex has a tendency to decompose in the distillation apparatus, thus resulting in the loss of rhodium by plating or precipitation on the surface of the process equipment.
The rhodium-containing catalyst may be recovered to a relatively great extent from the alcohol products of the hydroformylation reaction by treating the alcohol with various chemical compounds including ammonium hydroxide in either an aqueous or anhydrous state, with various nitrogen-containing compounds such as amines either primary, secondary or tertiary in nature, etc. In the event that an aqueous ammonium hydroxide solution is employed as a treating agent, the rhodium complex may be separated from the organic product phase and will be retained in the aqueous phase. The latter can then be recycled to the hydroformylation zone for use as a catalyst therein. However, the liquid product phase will still contain a trace amount of rhodium and therefore, it is necessary to recover or substantially decrease this trace amount of rhodium still present in said product. As will hereinafter be shown in greater detail, it has now been discovered that by contacting an organic reaction product with a solid adsorbent of the type hereinafter set forth in greater detail, it is possible to remove a relatively large amount of the trace metal present in said product and recover said metal for further use.